Mass spectrometer device and method using scanned phase applied potentials in ion guidance

Abstract

An ion guide or mass analyser is disclosed comprising a plurality of electrodes having apertures through which ions are transmitted in use. A pseudo-potential barrier is created at the exit of the ion guide or mass analyser. The amplitude or depth of the pseudo-potential barrier is inversely proportional to the mass to charge ratio of an ion. One or more transient DC voltages are applied to the electrodes of the ion guide or mass analyser in order to urge ions along the length of the ion guides or mass analyser. The amplitude of the transient DC voltage applied to the electrode may be increased with time so that ions are caused to be emitted from the ion guide or mass analyser in reverse order of their mass to charge ratio.

The invention claimed is: 
     
       1. An ion guide or mass analyser comprising:
 a plurality of electrodes; 
 means for applying a first AC or RF voltage to said plurality of electrodes so that at least some electrodes are maintained, in use, at opposite phases of said first AC or RF voltage; and 
 means for varying, switching, changing or scanning the phase difference or polarity of one or more electrodes so as to create, in use, an axial time averaged or pseudo-potential barrier along at least a portion of the axial length of said ion guide or mass analyser. 
 
     
     
       2. An ion guide or mass analyser as claimed in  claim 1 , wherein said means for varying, switching or changing the phase difference or polarity of said one or more electrodes is arranged to vary, switch, change or scan the phase difference or polarity by 0°, wherein 0 is selected from the group consisting of: (i) 0-10; (ii) 10-20; (iii) 20-30; (iv) 30-40; (v) 40-50; (vi) 50-60; (vii) 60-70; (viii) 70-80; (ix) 80-90; (x) 90; (xi) 90-100; (xii) 100-110; (xiii) 110-120; (xiv) 120-130; (xv) 130-140; (xvi) 140-150; (xvii) 150-160; (xviii) 160-170; (xix) 170-180; and (xx) 180. 
     
     
       3. An ion guide or mass analyser comprising:
 a plurality of electrodes; means for applying a n-phase AC or RF voltage to said plurality of electrodes wherein n≧2; 
 means for maintaining a first phase relationship or first aspect ratio between, at or of said plurality of electrodes; and 
 means for changing the phase relationship or aspect ratio between, at or of a sub-set of said plurality of electrodes so that a second different phase relationship or second aspect ratio is maintained between, at or of said sub-set of electrodes so as to create one or more axial time averaged or pseudo-potential barriers, corrugations or wells along at least a portion of the axial length of said ion guide or mass analyser. 
 
     
     
       4. An ion guide or mass analyser as claimed in  claim 3 , wherein n is selected from the group consisting of: (i) 2; (ii) 3; (iii) 4; (iv) 5; (v) 6; (vi) 7; (vii) 8; (viii) 9; (ix) 10; and (x)>10. 
     
     
       5. An ion guide or mass analyser as claimed in  claim 4 , wherein said first phase relationship or first aspect ratio has a first periodicity, pattern, sequence or value and wherein said second phase relationship or second aspect ratio has a second different periodicity, pattern, sequence or value. 
     
     
       6. An ion guide or mass analyser comprising:
 a plurality of electrodes; means for applying a n-phase AC or RF voltage to said plurality of electrodes wherein n≧2; and 
 means for scanning the phase or aspect ratio of one or more of said plurality of electrodes so as to create, in use, one or more axial time averaged or pseudo-potential barriers, corrugations or wells along at least a portion of the axial length of said ion guide or mass analyser. 
 
     
     
       7. An ion guide or mass analyser as claimed in  claim 6 , wherein n is selected from the group consisting of: (i) 2; (ii) 3; (iii) 4; (iv) 5; (v) 6; (vi) 7; (vii) 8; (viii) 9; (ix) 10; and (x)>10. 
     
     
       8. A mass analyser comprising:
 an ion guide including a plurality of electrodes having apertures through which ions are transmitted; 
 means for applying a first AC or RF voltage to at least some of said plurality of electrodes with axially adjacent electrodes or axially adjacent groups of the plurality of electrodes being supplied with opposite phases of said first AC or RF voltage and a plurality of first axial time averaged or pseudo-potential barriers, corrugations or wells having a first amplitude are created along at least a portion of an axial length of said ion guide; and 
 means for reversing the polarity of said first AC or RF voltage applied to at least a pair of axially adjacent electrodes or at least a pair of axially adjacent groups of the plurality of electrodes with one or more second axial time averaged or pseudo-potential barriers, corrugations or wells having a second amplitude being created along at least a portion of the axial length of said ion guide, wherein said second amplitude is different from said first amplitude. 
 
     
     
       9. A mass analyser as claimed in  claim 8 , further comprising:
 means for applying one or more transient DC voltages or potentials or one or more transient DC voltage or potential waveforms to said plurality of electrodes in order to drive or urge ions along at least a portion of the axial length of said ion guide. 
 
     
     
       10. A mass analyser as claimed in  claim 9 , further comprising:
 means for progressively decreasing in a linear, stepped or other manner the amplitude of said first AC or RF voltage so as to progressively reduce the amplitude of said one or more second axial time averaged or pseudo-potential barriers, corrugations or wells. 
 
     
     
       11. A mass analyser comprising:
 an ion guide comprising a plurality of electrodes; 
 a first voltage source configured to apply a first AC or RF voltage to at least some of the plurality of electrodes to create a plurality of first axial time averaged or pseudo-potential barriers, corrugations or wells having a first amplitude along at least a portion of an axial length of said ion guide; 
 a second voltage source configured to apply one or more transient DC voltages or potentials or one or more DC voltage or potential waveforms to at least some of the plurality of electrodes in order to drive or urge ions along at least a portion of the axial length of the ion guide; and 
 a third voltage source configured to apply a second AC or RF voltage to one or more of the plurality of electrodes to create one or more second axial time averaged or pseudo-potential barriers, corrugations or wells having a second amplitude, which is different from the first amplitude, along at least a portion of the axial length of the ion guide. 
 
     
     
       12. A mass analyser as claimed in  claim 11 , wherein said first voltage source is configured to supply axially adjacent electrodes or axially adjacent groups of electrodes with opposite phases of the first AC or RF voltage. 
     
     
       13. A mass analyser as claimed in  claim 12 , wherein said third voltage source is configured to supply axially adjacent electrodes or axially adjacent groups of electrodes with opposite phases of the second AC or RF voltage. 
     
     
       14. A mass analyser as claimed in  claim 11 , wherein said third voltage source is configured to supply axially adjacent electrodes or axially adjacent groups of electrodes with opposite phases of the second AC or RF voltage. 
     
     
       15. A mass analyser as claimed in  claim 11 , wherein said second voltage source creates a DC axial potential barrier or well employed in combination with at least one of the first or second axial time averaged or pseudo-potential barriers, corrugations or wells. 
     
     
       16. A mass analyser as claimed in  claim 11 , further comprising: one or more electrodes arranged at an entrance or exit of said ion guide for pulsing ions into or out of said ion guide. 
     
     
       17. A method of guiding ions or mass analysing ions comprising:
 providing an ion guide or mass analyser comprising a plurality of electrodes; 
 applying a n-phase AC or RF voltage to said plurality of electrodes wherein n≧2; and 
 scanning the phase or aspect ratio of one or more of said plurality of electrodes so as to create, in use, one or more axial time averaged or pseudo-potential barriers, corrugations or wells along at least a portion of the axial length of said mass analyser. 
 
     
     
       18. A method as claimed in  claim 17  further comprising allowing ions with mass to charge ratios ≧M1 exit the ion guide whilst axially trapping or confining ions with mass to charge ratios <M2 within said ion guide by said one or more axial time averaged or pseudo-potential barriers, corrugations or wells. 
     
     
       19. A method as claimed in  claim 17  further comprising translating a plurality of axial DC potential wells along the length of the ion guide or progressively applying a plurality of transient DC potentials or voltages to the electrodes along the axial length of said ion guide. 
     
     
       20. A method as claimed in  claim 17 , further comprising creating said plurality of first or second axial time averaged or pseudo-potential barriers, corrugations or wells at an upstream portion or an intermediate portion or a downstream portion of said ion guide.